The overall aim of the research is to further analyze by serologic means that region on Chromosome 6 of man which includes and surrounds the major histocompatibility loci (HLA). Primary emphasis will be directed toward the definition of the B lymphocyte antigens, DR, and their loci. Secondary attention will be on specificities of the HLA-A, B,C and D loci. The relationship of the DR antigens to disease susceptibility will be explored.